The present invention relates to a braiding or lace-making machine. This invention also concerns a method of operating such a machine.
A standard braiding machine has a stationary base on which is supported a lower ring rotor centered on and rotatable about a vertical axis. This lower ring carries an annular array of filament supplies and has a guide with an annular upwardly directed surface centered on the axis. An upper rotor centered on the axis has slides riding on the lower ring surface and itself carries an annular array of filament supplies. A drive is connected to the rotors to rotate them in opposite directions about the axis so that the upper ring slides on the lower ring. Filaments are pulled axially up off the supplies to form a central braid, typically a cable or hose.
The upper slides and the lower-ring guide can therefore move relative to each other at very high speed. In a system working at 150 RPM the relative speed can be as much as 5 m/sec. Since this is a simple slide joint, it is essential to lubricate the interface between the guide and slides to prevent excessive heat build-up and wear. Thus systems are provided which pump a lubricant oil of some sort to the slide joint, normally at several sites spaced angularly around it.
The problem with this system is that if insufficient lubricant is applied, the joint will heat and possible seize up. Alternately if too much lubricant is pumped into the joints, it will be driven centrifugally out and can contaminate the filaments being braided together. While in a system making a bridge cable, some oil might not be a problem, when the braid is intended for medical use, it must be perfectly clean so no such contamination is permitted. Providing the right amount of lubricant is therefore a delicate problem.
German patent 4,111,553 of J. Lache proposes a system with individual piston-type dosing units for the individual lubrication sites that allow very accurate control of the amount of lubricant dispensed at these sites. Experimentation determines the right amount which is then normally set for an entire operational cycle, with at most the worker checking in to see if lubricant was being sprayed out, in which case the dose would be decreased, or the joint was drying out, in which case the dose would be increased. The system required close monitoring by the operational personnel add at best approximated the ideal level of lubrication.
German patent 195 23 721 of J. Lache has pressure-increasing units provided near the individual lubrication sites. These units take over the role of the individual dosers of above cited German ""553. The pressure-increasing units are operated by pulses whose frequency increases with rotation rate of the braiding machine, to produce some sort of correspondence between lubrication rate and lubrication need. Since, however, such units must operate at a certain minimum pressure, they cannot readily accommodate low rotation speeds or particularly light rotors, so that in these cases the lubrication is often excessive, spraying droplets of oil onto the workpiece.
It is therefore an object of the present invention to provide an improved braiding machine.
A further object is the provision of an improved method of operating a braiding machine.
Another object is an improved braiding system where the machine is lubricated sufficiently to reduce wear but not so much as to allow excess lubricant to soil the workpiece.
A braiding machine has a pair of rotors that are rotated relative to each other with one of the rotors forming a guide on which slides of the other rotor slide. A temperature of an interface between the slides and guide is continuously monitored. Lubricant to the interface at a rate only sufficient to prevent the sensed temperature from exceeding a predetermined limit.
Thus with this system a desired operating temperature, e.g. 60xc2x0 C., at the interface is established and, when the temperature starts to rise above this level the lubricant-feed rate is increased. If the temperature starts to drop, the lubricant-feed rate is decreased. In this manner the system avoids the standard practice of simply feeding in so much lubricant that the slides and guide are protected, even though in many cases this is so much extra lubricant that it sprays radially out from the slide/guide interface and contaminates the filaments.
It is known from Japanese patent document 32 09 508 of Takada Hirotoshi to provide a temperature-sensitive valve for dispensing a lubricant in accordance with the temperature at the valve, but such a system cannot be mounted on the rotor of a braiding machine. Similarly U.S. Pat. No. 4,336,905 of Zirps describes a control valve for maintaining a pressure medium at a constant temperature and viscosity, but such an arrangement is also not suitable for mounting in a braiding machine.
The load exerted by the rotors on a drive rotating the rotors is monitored according to the invention. Thus if, for instance, the filament being braided sheds abrasive particles that get into the slide/guide interface, the system will be able to respond with extra lubrication, preventing excess wear of these parts even if they are not overheating. This load-responsive system is also advantageous to compensate for a momentary high load, as for instance if something gets caught briefly in the interface.
The rate is also varied in accordance with the monitored drive load. Thus as the supplies of filament carried by the rotors, typically large spools of cord or wire, are used up and the rotors get lighter, the lubrication rate is adjusted downward as there is less pressure at the slide/guide interface.
The controller according to the invention can also vary drive speed if necessary, for instance in case of a blockage. Furthermore a cooling fan can be operated by the controller in certain circumstances.
Similarly a rotation speed of the drive rotating the rotors can be monitored so as to vary the rate in accordance with the monitored drive speed. Thus until the system gets up to speed, the lubrication level is held low. This speed-responsive system is particularly important in determining the minimum lubrication level needed by the machine.
It is also possible to vary the rate in accordance with an inputted weight of the rotors. Thus the operator of the machine keyboards into the controller the number of filament supplies and how much each one weighs so the machine knows right from the start how much friction it will be dealing with.
The lubricant is fed in accordance with the invention in separate doses at intervals and the lengths of the intervals are varied to change the lubricant-feed rate. Thus each dose is the same; it is the time between doses that is varied. This dosing is done by turning on and off a pump.
Furthermore according to the invention an output is generated corresponding to the sensed temperature at the interface and the output is compared with a set point to establish the lubricant-feed rate.
The braiding machine according to the invention therefore has a support defining an upright axis, a lower rotor rotatable on the support about the axis and defining an annular guide centered on the axis, and an upper rotor having slides bearing at an interface on the guide and rotatable on the lower rotor about the axis. A drive connected to the rotors rotates same in opposite directions about the axis with the slides sliding on the guide. Dosers feed a lubricant to the interface and a sensor detects a temperature of the guide at the interface. A computer-type controller connected to the doser and to the sensor feeds the lubricant to the interface at a rate only sufficient to prevent the detected temperature from exceeding a predetermined limit.
The controller is connected to the drive for varying the lubricant-feed rate in accordance with rotor speed. This can be done by means of a frequency converter connected to the drive motor. Similarly the controller can be connected to the drive for varying the lubricant-feed rate in accordance with a load the rotors exert on the drive.
The dosing system includes a lubricant supply and a pump connected thereto. The controller periodically actuates the pump to force lubricant into the interface.
This interface according to the invention is provided with a plurality of lubricating sites. The dosing system includes respective pressure-operated dosers connected to the sites and to the pump.
The sensor is fixed in the guide and conductors including commutator rings on the lower rotor connect the sensor to the controller.
The system of this invention can be applied to a standard or figure-type braiding machine. It can also be used on machines for knitting, weaving, or making bone lace.